Express 2500 V8-5.3L VIN T (2005)
Speedometer Head: Description and Operation
SPEEDOMETER
The instrument panel cluster (IPC) displays the vehicle speed based on the information from the powertrain control module (PCM). The PCM calculates
the vehicle speed from the vehicle speed sensor (VSS) circuit. The IPC receives a class 2 message from the PCM indicating the vehicle speed. The PCM
also calculates the vehicle speed based on the wheel reference vehicle speed class 2 message from the electronic brake control module (EBCM). The
PCM uses the vehicle speed information from the EBCM as a backup. The IPC displays the vehicle speed information from the EBCM when the PCM
detects a malfunction in the vehicle speed sensor circuit.
The speedometer defaults to 0 km/h (0 mph) if the IPC detects a loss of class 2 communications with both the PCM and the EBCM.
